Information recently shared on the HomDGCat Wiki in addition to the Genshin Impact Leaks subreddit gives us a detailed look at the upcoming Imaginarium Theater lineup in Genshin Impact showing us which characters and enemy lineup we can expect to see in the 6.1 update.

What is the Imaginarium Theater in Genshin Impact?
The Imaginarium Theater in Genshin Impact is a challenging endgame combat mode introduced in Version 4.7. Imaginarium Theater features a theater-themed structure where players build a team of characters to battle through multiple acts with unique enemy waves and stage effects.
Each season limits which characters can be used featuring trial characters and special invitation characters which allow you to use characters that arent the current element. This encourages players to use creative team building and strategy focuses. Completing acts rewards such as Primogems, materials, and exclusive cosmetics, offering another endgame mode like Spiral Abyss.
What We Know About V6.1 Imaginarium Theater
The Imaginarium Theater update for Genshin Impact Version 6.1 introduces a lineup of challenges centered around the Pyro, Cryo, and Anemo elements. This season highlights Klee, Bennett, Citlali, Diona, Chasca and Sucrose as the opening characters, while Mualani, Mona, Albedo and Fischl appear as special invitation options.
Players will face a variety of tough bosses including Electro Primo Geovishap, Thunder Manifestation, Solitary Suanni, Secret Source Automaton: Overseer Device, Consecrated Scorpion and Consecrated Fanged Beast each with distinct combat styles. The mode continues to offer a dynamic, strategic endgame experience focused on creativity, team synergy, and mastery of different elements.